1. Field of the Invention
This invention relates to a method of permanently bonding two surfaces, at least one surface being a resin selected from the group consisting of an elastoplastic organopolysiloxane resin and a polytetrafluoroethylene resin using a curable adhesive based upon polyorganosiloxanes, the method being useful in the production of air supported or tensioned structures.
2. Description of the Prior Art
In the construction of tension supported structures and air supported structures, it is necessary to fasten pieces of plastic sheet or coated fabric to each other to form seams and to fasten the pieces to the support structure. Seams have been made in thermoplastic sheets by heat fusion and by adhesive bonding. Fiberglass fabric coated with polyorganosiloxane has been used in outdoor applications such as greenhouses because of its excellent weatherability. Because it is a thermoset material the polyorganosiloxane coated fiberglass can not be bonded by heat fusion. Polyorganosiloxane coated fabric has been bonded together by the use of polydiorganosiloxane adhesives.
Adhesives of various types have been commercialized which are based upon silicone polymers. They have been successful because they adhere to a great variety of surfaces and because the adhesives themselves are able to function over a wide temperature range. Types of adhesives which have been commercialized include pressure sensitive adhesives, permanent adhesives and moisture curing one-part adhesives.
In U.S. Pat. No. 2,736,721, issued Feb. 28, 1956, Dexter teaches that a composition comprising a mixture of benzene soluble resin copolymer and a diorganopolysiloxane having a viscosity of at least 1,000 Pa.s gives excellent adhesives. His mixtures, which may also contain titanium esters and catalysts are used by applying the adhesive to a surface to be adhered, curing the adhesive, then placing the surfaces to be adhered together. The adhesive is stated to adhere to any known solid surface. When used to make adhesive tapes, they are of the class known as pressure sensitive adhesives. The tape with the cured adhesive is pressed firmly against a surface and adheres to it, there is no further cure required.
In U.S. Pat. No. 2,814,601, issued Nov. 26, 1957, Currie and Keil teach siloxane compositions which are useful as pressure sensitive adhesives and as permanent bond adhesives. Their compositions relate to a composition of matter composed essentially of a benzene soluble resin copolymer of SiO.sub.2 units and R.sub.3 SiO.sub.0.5 units and a hydroxyl end-blocked diorganopolysiloxane fluid of from 5 to less then 1000 Pa.s viscosity. To prepare an adhesive which will give a permanent bond, they include crosslinking agents which are alkylpolysilicates and/or hydrogen bearing siloxanes of the formula R.sub.n H.sub.m SiO.sub.(4-n-m)/2 and a curing catalyst which includes metallic salts of carboxylic acids. The permanent bonds are formed by mixing the above ingredients shortly before use, commonly including a solvent, then coating the adhesive over each surface to be joined. The solvent is allowed to evaporate until a tacky film is obtained, then the two surfaces to be bonded are brought together, and the adhesive is allowed to cure.